Heavy snowfall on Thursday with strong winds and mild temperatures is expected to form widespread storm slabs and drive the danger to HIGH. Travel in avalanche terrain is not recommended.
Weather Forecast
The last major low pressure system is expected to bring heavy snowfall to the region Wednesday overnight and Thursday. 15-25 cm is expected Wednesday overnight and 30-50 cm is expected on Thursday. Alpine wind is forecast to be strong to extreme from the southwest on Thursday and freezing levels are expected to reach around 800 m elevation. Mostly dry and sunny conditions are expected for Friday with light alpine wind and freezing levels around 600 m. A weak storm pulse is forecast to bring around 5 cm of snow on Saturday with strong alpine wind from the northwest.
Avalanche Summary
A widespread natural avalanche cycle was observed on Monday evening and overnight. These were storm slab avalanches up to size 2 with a typical slab thickness of 20-40 cm. No new avalanches were observed on Tuesday. On Thursday, another natural avalanche cycle is expected similar to the one that occurred on Monday night. Heavy snowfall and mild temperatures are expected to quickly form new slabs. In wind exposed terrain, expect thick touchy slabs in leeward terrain features.
Snowpack Summary
30-50 cm of new snow has accumulated since Monday. This new snow sits over a variable interface which consisted of wind affected surfaces, faceted (sugary) snow, or surface hoar. Recent reports suggest this storm snow is now well bonded except places where surface hoar may be preserved. Recently strong southerly winds have formed new wind slabs in leeward and cross loaded features in wind exposed terrain. A crust that formed a week ago is likely down around 50-70 cm. Below this crust, the snowpack is generally considered well settled and stable.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.